Thanks for your reply. All steps previously done and after a week the car says "replace 12v battery".
I didn't perform the battery test because I don't have that gadget but I managed to recharge with a car battery charger and it takes sometimes only 30 minutes to charge from 12,6V to full indication and other times 1h30 (which is more normal) but I think it should need about 6-8h for a discharged 45Ah battery to go to full...
Well, this will be easier if the online shop where I bought the varta were more proactive to let me send it them for a test but they are doing all they can't do to not to do that haha.